This invention relates to drilling generally horizontal boreholes in subterranean formations such as coal seams, and more particularly to a device which facilitates pumping a survey probe into a borehole to determine the position of the borehole relative to a coal seam.
Coal seams often contain methane gas in amounts which affect the safety of a mining operation. One method of alleviating the methane gas problem is to drill one or more boreholes into the seam in advance of mining, and to produce gas through the borehole until the methane gas level is low enough to permit safe mining. It is essential in such an operation to maintain the borehole within the coal seam, and techniques have been devised to provide this capability. One such technique utilizes a survey probe which contains instrumentation capable of providing information regarding the borehole position. Such probes are periodically pumped down the interior of the drill rod to a position adjacent the drill bit, readings are taken, and the survey probe is then removed from the drill rod. If necessary, adjustments are made in the drilling operation, based on the information obtained, to maintain the borehole within the coal seam.
Prior to this invention, the placement and removal of the survey probe in and from the drill rod was a time-consuming procedure involving threading a water seal onto a drill motor and utilizing an inconvenient amount of valves and hoses.